Centrifugal pumps of the type with which it is generally contemplated that the improved sealing arrangements of the present invention will be employed typically include a radially-outer fixed pan or seat and a radially-inner part or element that operatively rotates with the pump shaft and relative to the seat. Mechanical planar seals are developed by directing the pumped medium, or another supplied liquid, into the spacing between the opposed, radially inner and outer member surfaces, and allowing a small amount of the medium or liquid to flow and leak out from between the sealing surfaces. This leakage is not normally visible as the liquid evaporates; however, the result of such leakage is that impurities in the liquid, such as (and especially) crystallized salts, accumulate outside of and adjacent to or around the seal. Such accumulations are accompanied by a notably increased risk that the fixed surface will be unintendedly contacted by or clutched to the rotating surface and thereby caused to rotate with the shaft, or that the sealing surfaces will be undesirably forced away from each other thus resulting in rapid leakage or loss of the pumped medium or supplied liquid with which the seal is developed and maintained. In order to prevent such occurrences the outside or exterior side of the seal is flushed or cleaned with a so-called quench or flushing liquid, typically comprised of pure water. As this quench-water or liquid cannot be permitted to uncontrollably splash out or away from the area that it is intended to clean, the sealing assembly is generally additionally provided with a secondary seal which, in its most simplified form, may be implemented by a radial sealing ring. Labyrinth seals and so-called lip seals and pack boxes with box braidings or graphite rings are also sometimes employed to form the secondary seal. In any event, all of these sealing rings and pack boxes and the like require a continuous supply of liquid for lubrication and cooling but will nevertheless wear out and begin to leak after use for only a relatively short period of time.
The secondary seal may also comprise a further mechanical planar seal, thus providing a double mechanical planar seal arrangement. Such double mechanical planar seals are significantly more costly to implement and their design often requires maintenance of an over-pressure condition in the seal housing in which it is located. As a consequence, any shortfall in the supply of sealing liquid to the sealing surfaces and structures will prove catastrophic as the inner seal may be forced out, with attendant leakage of the pumped medium, and the outer seal will run dry and overheat in very short order.